Oxalic acid manufacture

ABSTRACT

THE PRESENT INVENTION RELATES TO A NOVEL PROCESS FOR PREPARING OXALIC ACID. MORE PARTICULARLY, IT RELATES TO THE NOVEL OXIDATION OF ACETYLENE UTILIZING ALKALI METAL FERRICYANIDE AND EITHER OSMIUM TETRAOXIDE OR AN ALKALI METAL OSMIATE TO PREPARE CORRESPONDING OXALIC ACID. STILL MORE PARTICULARLY, THE INVENTION IS CONCERNED WITH THE ELECTROLYTIC OXIDATION OF AN ALKALI METAL FERROCYANIDE   (M4FE(CN)6**3H20   WHERE M IS AN ALKALI METAL, SUCH AS SODIUM OR POTASSIUM) TO OBTAIN AN AQUEOUS ALKALINE SOLUTION OF ALKALI METAL FERRICYANIDE (M2FE(CN)6), ADDING THERETO A SUITABLE CATALYTIC QUANTITY OF EITHER OSMIUM TETRAOXIDE OR AN ALKALI METAL OSMIATE WHILE INTRODUCING ACETYLENE INTO THE LATTER SOLUTION, AND RECOVERING RESULTANT OXALIC ACID IN GOOD YIELD AND PURITY.

United States Patent 3,555,084 OXALIC ACID MANUFACTURE Jaspal Singh Mayell, Stamford, Conn., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Filed Aug. 1, 1967, Ser. No. 657,490 Int. Cl. C07c 55/06 US. Cl. 260533 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a novel process for preparing oxalic acid. More particularly, it relates to the novel oxidation of acetylene utilizing alkali metal ferricyanide and either osmium tetraoxide or an alkali metal osmiate to prepare corresponding oxalic acid. Still more particularly, the invention is concerned with the electrolytic oxidation of an alkali metal ferrocyanide It has been unexpectedly found that oxalic acid can be prepared in a straightforward manner, in high yield substantially free from explosions while utilizing an aqueous environment. In brief, oxalic acid is directly produced in good yield by introducing acetylene into an aqueous alkaline solution of potassium or sodium ferricyanide containing catalytic amounts of osmium tetraoxide. The potassium ferricyanide and alkali which are consumed in producing the oxalic acid are electrochemically regenerated when utilizing an oxygen-depolarized cathode. Hence, based on the amount of potassium ferricyanide actually consumed during the formation of oxalic acid, yields of 30%, or higher, are attained.

According to the process of the invention, an aqueous solution comprising from 1%-25% of an alkali metal ferrocyanide, such as potassium ferrocyanide or sodium ferrocyanide, is electrochemically oxidized to the corresponding alkali metal ferricyanide employing a conven tional electrolytic cell. To the latter electrolyzed solution are added catalytic amounts of osmium tetraoxide or an alkali metal osmiate, usually from about 0.001% to about 1.0%, based on the initial weight of alkali metal ferricyanide in the reaction mixture. There is next introduced acetylene at a rate equal to from 1 to 5 liters per hour for from /2 to 2 hours, whereby oxalic acid is formed and separated from the solution. During the formation of oxalic acid, the alkali metal ferricyanide is reduced to alkali metal ferrocyanide in solution. The ferrocyanide thus formed is finally regenerated electrolytically to'alkali metal ferricyanide.

In general, the overall reaction can be conveniently carried out in any electrolytic cell into which an aqueous solution of an alkali metal ferrocyanide is initially introduced. The latter is oxidized to alkali metal ferricyanide by establishing a potential across two liquid-impervious electrodes, at least one of such electrodes being gas-pervious. The electrodes are prepared from graphitic carbon and small amounts of polytetrafiuoroethylene. A potential across the cell from about 0.5 volt to about 1.60 volts is next established by employing constant current from about 5 milliamperes/cm. to about 30 milliamperes/cm. Preferably, any oxygen-containing gas, such as air or oxygen, is permitted to contact the surface of one of the negatively designated electrodes, whereby the alkali metal ferrocyanide aqueous solution is converted to an alkali metal ferricyanide and an alkali metal hydroxide.

The gas-permeable, liquid-impermeable negative electrode or cathode employed in the process of the present invention can advantageously be prepared from an electrically conductive material, such as carbon, to which there is added a noble metal or other active metal catalyst. Further, a metallic screen may be impressed on the electrode and a suitable electrical lead then attached thereto. in order to avoid any electrolyte flowing into the zone into which the oxygen-containing gas is introduced, the cathode is backed, for instance, with a porous polytetrafluoroethylene sheet, thereby permitting only the oxygencontaining gas to flow through the electrodes backing. If desired, the cathodes surface fronting the electrolyte can be modified with an ion-exchange resin membrane, such as, for instance, either a copolymer of styrene sulfonic acid on polytetrafiuoroethylene or a copolymer of acrylic acid on polyethylene.

The positive electrode or anode can be prepared, for instance, by admixing a suitable water-proofing agent, such as an aqueous emulsion of polytetrafluoroethylene, with a conductive material, such as carbon, to which may optionally be added, if desired, a suitable metallic substance, such as platinum, and molding the same. To obtain an electrode of increased strength, the mixture comprising carbon particles and an emulsion of polytetrafluoroethylene is spread on a metallic screen, such as tantalum, and molded. Resultant electrode is finally pressure-backed by a non-porous polytetrafluoroethylene sheet, so as to prevent any leakage of electrolyte from the cell.

The following examples are presented to illustrate preferred embodiments of the invention. These are not to be taken as limitative.

EXAMPLE 1 To a suitable electrolytic cell comprising a compartment for receiving electrolyte, a 6 x 6 inch gas-pervious, liquid-impervious graphitic carbon containing about 5% polytetrafluoroethylene, positioned on two sides of said compartment, and means for contacting one electrode with oxygen as well as means for imposing a potential thereon, are added 42 grams of potassium ferrocyanide dissolved in one liter of water. The solution is electrolyzed for one-half hour at a constant current of 6.0 amperes equivalent to a current density of 25 ma./cm. On analysis, the electrolyzed solution contains 33 grams of potassium ferricyanide and 5.6 grams of potassium hy droxide. The pH of the solution is 13.

To the resultant solution is added 0.03 gram of osmium tetraoxide. Thereafter, acetylene is introduced into the catalyzed solution at a rate equal to three to four liters over a two-hour period. Resultant solution is acidified with hydrochloric acid and oxalic acid is extracted by liquid-liquid extraction with ether. There is recovered a yield of 20% of oxalic acid, based on the consumption of the alkali metal ferricyanide to the alkali metal ferrocyanide. Thereafter, the remaining reaction mixture is regenerated by subjecting the same to electrolysis to once again effect conversion of the ferrocyanide to ferricyanide.

EXAMPLE 2 is recovered in 30% yield based on the consumption of alkali metal ferricyanide to the alkali metal ferrocyanide. Thereafter, the remaining reaction mixture is subjected to electrolysis to recover ferricyanide and potassium hydroxide from potassium ferrocyanide.

Advantageously, the process of the invention is equally applicable to the conversion of homologs of acetylene, such as, for example, n-propyliclyne or n-butylidyne, to their corresponding acids.

I claim:

1. A process for preparing oxalic acid which comprises: incorporating acetylene into an aqueous alkaline solution containing an alkali metal ferricyanide and catalytic amounts ranging from 0.001 percent to 1.0 percent of an alkali metal osmiate or osmium tetraoxide, and recovering oxalic acid directly from the resultant solution.

2. The process according to claim 1 wherein the alkali metal ferricyanide is potassium ferricyanide.

3. The process according to claim 1 wherein the pH of the reaction solution is established between 8 and 13.

4. A process for preparing oxalic acid according to claim 1 which comprises the steps of: oxidizing an aqueous solution of alkali metal ferrocyanide to an alkali metal ferricyanide and establishing a pH of the resultant oxidized solution at from 8 to 13, incorporating in said solution a catalytic amount ranging from 0.001 percent to 4 i l 1.0 percent of an alkali metal osmiate or osmium tetra- OXide, passing acetylene into the so'catalyzed solution and, thereafter, recovering oxalic acid from the resultant solution.

5. The process according to claim 4 wherein potassium osmiate is present in an amount equal to 0.001% to 1.0% based on the initial weight of alkali metal ferricyanide in the reaction mixture prior to oxalic acid formation.

6. The process according to claim 4 wherein the alkali metal ferrocyanicle which is electrolytically oxidized is potassium ferrocyanide.

References Cited UNITED STATES PATENTS 3,428,675 2/1969 Brossard et al. 260533 3,352,768 11/1967 KatZ et al. 260537 FOREIGN PATENTS 720,416 10/1965 Canada 260-533 LORRAINE A. WEINBERGER, Primary Examiner E. J. SKELLY, Assistant Examiner US. Cl. X.R. 2049l 

